Method and device for applying compressive and/or tractional forces to essentially rod-shaped workpieces consisting of electroconductive and/or magnetisable material

ABSTRACT

The disclosure relates to a method for applying compressive and/or tractional forces to an essentially rod-shaped workpiece, according to which a mechnical engagement in the rod-shaped workpiece can be avoided. To this end, the method involves applying compressive and/or tractional forces to an essentially rod-shaped workpiece including an electroconductive and/or magnetizable material. A magnetic field is applied to the workpiece, including a gradient in the direction of the force to be applied. The disclosure also relates to a device for applying compressive and/or tractional forces to an essentially rod-shaped workpiece including electroconductive and/or magnetizable material. The device includes a coil arrangement that is supplied by a current and is designed to produce a magnetic field having a gradient.

The invention relates to a method for applying compressive and/ortractive forces on an essentially rod-shaped workpiece consisting ofelectrically conductive and/or magnetizable material. The inventionmoreover relates to a device for executing the method.

Essentially rod-shaped workpieces in the sense of this invention aresuch workpieces whose expansion in the axial direction clearly exceedsthe dimensions in the lateral directions. This can be for example pipes,rods, bars, profile struts or flat strips.

To move such workpieces for example within the framework of a machiningor manufacturing system, it is necessary to apply compressive and/ortractive forces on these workpieces. Similarly such forces are necessaryespecially during forming processes where the workpieces for example arepressed or pulled through molding dies to develop the profile or changethe diameter. This is required e.g. when drawing pipes, wherein a pipewith a diameter D1 before the drawing process is formed by being pulledthrough a die or a drawing plate while shaping the material into a pipewith a smaller diameter D2 than the diameter D1. For such an operationit is necessary to apply an appropriate tractive force on the workpieceto be formed, in the example mentioned this is the pipe that is to bedrawn, in order to achieve on one hand the shape and on the other hand aconveying process of the workpiece to be formed. In familiar formingsystems, for example for drawing pipes, this is generally accomplishedmechanically. A gripper grabs the workpiece on one end that is guidedthrough the forming device, for example the drawing die, and is moved inthe direction of traction by means of a mechanical drive, such as anelectric motor. This way the tractive forces required for the formingprocess are generated, which can amount to for example 10 tons. Knownmechanical facilities, however, have the disadvantage that a tractiveelement always must be attached to the rod-shaped workpiece to beformed, which is associated with considerable effort. Moreover, withsuch mechanical tractive elements, the speed of the drawing process islimited due to mechanics. In typical pipe drawing systems, this is, forexample, a maximum of 300 m pipe material per minute. This is especiallydisadvantageous with so-called continuous drawing machines, where aquasi-continuous workpiece such as a wound pipe of great length is drawncontinuously to be formed.

Proceeding from this prior art, it is the object of the invention tooffer a method for applying compressive and/or tractive forces on anessentially rod-shaped workpiece where the use of mechanical grippingelements can be foregone. Moreover a device for executing such a methodshall be provided.

To accomplish this objective, the invention suggests a method forapplying compressive and/or tractive forces on an essentially rod-shapedworkpiece consisting of an electrically conductive and/or magnetizablematerial, whereby a magnetic field is applied to the material having agradient in the direction of the force to be applied.

By applying a magnetic field comprising a gradient pointing in thedirection of the force to be applied to the rod-shaped material, amagnetic field is generated in the electrically conductive and/ormagnetizable material through a flow of current initiated by inductionor through an alignment of magnetic poles. Due to this induced magneticfield and the gradient of the outer magnetic field, a force that ispointed in the direction of the gradient of the outer magnetic field isapplied on the rod-shaped workpiece. Depending on the alignment of thegradient of the outer magnetic field, a compressive force pointing inone direction or a tractive force pointing in the opposite direction canconsequently be applied on the workpiece. Applying the forces does nottake place mechanically, but purely through the interaction of the outermagnetic field with the magnetic field induced in the material of theworkpiece based on this field.

Since with such a method of applying compressive and/or tractive forcesmechanical motion is not required, with this method for example anadvancing speed during the forming process is not limited by mechanicalspecifications. Consequently basically higher speeds can be reached thanis the case with systems known from the state of the art.

Pursuant to a beneficial development of the invention, the magneticfield comprising a gradient can be generated by a coil arrangementsubjected to current through flow, having an inhomogeneous construction.An inhomogeneous design of a coil arrangement within the meaning of thisinvention can be realized by a single coil having an inhomogeneousshape, for example an interior tapering down conically in thelongitudinal direction of the coil, or a winding density that changes inthe longitudinal direction of the coil, thus generating an inhomogeneousmagnetic field. A coil arrangement consisting of several coils deviatingfrom one another in their properties, however, should also be understoodby an inhomogeneous construction of a coil arrangement. Such a coilarrangement allows a magnetic field comprising a gradient to begenerated in a simple manner, whereby the coil arrangement itself isfixed in space, and the magnetic field is generated by conducting a flowof current through the coil arrangement. Such a coil arrangementrequires no mechanically moving parts whatsoever; the compressive and/ortractive forces are applied on the workpiece exclusively due to themagnetic fields generated by the coil arrangement.

In accordance with another advantageous refinement of the invention, itis provided that the magnetic field comprising a gradient is generatedby at least two coils that are arranged around the rod-shaped workpiece,whereby the coils are subjected to current through flow, respectively,for the generation of different magnetic fields. A coil within themeaning of the invention should hereby also be understood as individualconductive loops. Within the framework of this embodiment of theinvention two coils of equivalent design can be arranged around theworkpiece, axially spaced from each other, whereby for the purpose ofgenerating different fields currents of different strengths and/orphases are conducted through the coils. When the magnetic fieldcomprising a gradient is created with such an arrangement, it ispossible, with a large number of coils and suitable control, to achievea very exactly controlled course of the magnetic field, which enables anexactly metered application of compressive and/or tractive forces on therod-shaped workpiece.

For the controlled application of compressive and/or tractive forces onthe rod-shaped workpiece, pursuant to the method described here in anadvantageous refinement of the same, the current flowing through thecoils and/or the coil arrangement can be modified as a function of thetime. This can occur periodically, whereby the selected frequency ispreferably selected in accordance with a frequency of resonance that isdesigned as a function of the material properties and the dimensions ofthe rod-shaped workpiece. The frequency at which the most efficientconversion of electric energy into compressive and/or tractive forcesoccurs with the selected coil arrangement with interposition of themagnetic fields is designated as such a frequency of resonance.

In order to prevent the coil arrangement from overheating, the coils canbe cooled, if necessary, pursuant to a suggestion of the invention.

Pursuant to another advantageous refinement of the invention, therod-shaped workpiece, if it is electrically conductive, can be subjectedto current through flow to support the application of compressive and/ortractive forces. By connecting the workpiece itself with an externalsource of power and thus supplying it by a current, apart from themagnetic field that is induced by the exterior magnetic field anothermagnetic field is generated around the workpiece. An amplification ofthe force applied to the workpiece can be attained depending on thedirection of the current flow and the polarity of the exterior magneticfield.

The workpiece can be cooled in accordance with another advantageousproposal of the invention in order to prevent the workpiece fromoverheating due to the external magnetic field, as this can occurespecially in the case of periodically alternating magnetic fields.

With the method of the invention, rod-shaped workpieces can betransported or be drawn or compressed by corresponding forming dies forthe purpose of shaping them. The rod-shaped workpieces only have toconsist of an electrically conductive and/or magnetizable material. Hereall electrically conductive materials come into consideration, but alsomagnetically polarizable and/or magnetizable resins or equivalentmaterials.

To accomplish the aforementioned objective, the invention furthermoreproposes a device for applying compressive and/or tractive forces on anessentially rod-shaped workpiece consisting of electrically conductiveand/or magnetizable material, comprising a coil arrangement that can beacted by a current for creating a magnetic field comprising a gradientpointing in the direction of the force to be applied on the workpiece.

The coil arrangement here can comprise a single, inhomogeneouslydesigned coil. However it preferably comprises at least two coils, whichcan be acted by a current that can be adjusted individually for eachcoil. Coils within the meaning of the invention should be understood notonly as coils with several windings, but also individual conductorloops. Pursuant to an advantageous refinement of the invention, theindividual coils are arranged concentrically around a workpiece pathaxially spaced from one another, along which the workpiece is to beacted upon by compressive and/or tractive forces.

Further advantages and features of the invention are disclosed to theexpert from the following description of on exemplary embodiment basedon the sole appended FIGURE, wherein:

FIG. 1 illustrates in diagrammatic view an arrangement for drawing apipe, whereby the tractive force required for the drawing operation isapplied on the pipe by means of the inventive method.

FIG. 1 shows a diagrammatic view of a section of a pipe 1. The pipe 1 isshown as it is drawn through a die 4 in the direction of the arrow 8 forthe purpose of reducing the pipe diameter. A pipe section 2 with theinitial diameter of the pipe is shown in the figure to the left of thedie 4. In the figure to the right of the die 4, a pipe section 3 isshown, which has a reduced diameter as compared to the diameter of thepipe section 2. Moreover a coil arrangement 5 is depicted, which iscomposed of a total of four equivalent coils 5 a through 5 d, which arearranged in the axial direction of the pipe 1 at a distance from eachother and concentric to the pipe section 3 around said section. Thecoils 5 a through 5 d of the coil arrangement 5 are connected with acontrollable power source 7 by means of electric lines 6 a through 6 d.

With the controllable power source 7, individually different currentscan be supplied to the coils 5 a through 5 d of the coil arrangement 5by means of the electric lines 6 a through 6 d so as to create amagnetic field in the area of the coil arrangement 5 with a gradientrunning in the direction of the arrow 8. Such a magnetic fieldcomprising a gradient induces a secondary magnetic field in the pipesection 3 of the pipe consisting of an electrically conductive and/ormagnetizable material. Due to the interaction between the magnetic fieldprovided with a gradient that is generated by the coils 5 a through 5 dand the secondary magnetic field a force is generated, which in theexample shown acts in the direction of the arrow 8 on the pipe section 3and thus on the pipe 1. The pipe 1 is drawn through the die 4 and formedwith the help of this force.

The controlled power source 7 here can be operated such that thecurrents flowing through the coils 5 a through 5 d, respectively, can bevaried with respect to time, whereby the currents conducted in the lines6 a through 6 d each can have different amounts and/or can beout-of-phase.

With the arrangement depicted in a diagrammatic view in the exemplaryembodiment, a tractive force can also be applied on the pipe for thepurpose of drawing a pipe without mechanical aids. The tractive forcethat is required for drawing the pipe is generated solely due to theprimary magnetic field that is generated with the coil arrangement andthe secondary magnetic field that is induced in the electricallyconductive and/or magnetizable material of the pipe. Instead of applyinga tractive force on the pipe, a coil arrangement corresponding to thecoil arrangement 5 could be arranged on the pipe section 2 depicted inthe left of the figure, wherein the coils 5 a through 5 d should beswitched such that a compressive force that also acts in the directionof the arrow 8 is exerted on the pipe end 2.

The embodiment shown serves only to explain the invention and is notrestrictive. The coil arrangement 5 in particular can comprise a numberof coils that differs from the four depicted coils 5 a through 5 d.Also, to reinforce the generated compressive and/or tractive force, apipe consisting of conductive material can be connected to the powersource and thus be subjected to current through flow.

LIST OF REFERENCE NUMBERS

-   1 Pipe-   2 Pipe Section-   3 Pipe Section-   4 Die-   5 Coil Arrangement-   5 a Coil-   5 b Coil-   5 c Coil-   5 d Coil-   6 a Electric Line-   6 b Electric Line-   6 c Electric Line-   6 d Electric Line-   7 Controlled Power Source

1-13. (Cancel)
 14. Method for applying compressive and/or tractiveforces on a rod-shaped workpiece comprising electrically conductiveand/or magnetizable material, the method comprising: applying a magneticfield on the workpiece comprising a gradient pointing in a direction ofa force to be applied, wherein a current flowing through a coilarrangement is modified periodically as a function of time with afrequency that corresponds to a resonance frequency for a maximum forceto be applied on the workpiece.
 15. Method pursuant to claim 14, whereinthe magnetic field is generated by the coil arrangement comprising atleast two coils that are arranged around the workpiece axially spacedfrom each other, wherein wherein the at least two coils are flowedthrough by a current, respectively, for the purpose of generatingdifferent magnetic fields.
 16. Method pursuant to claim 15, wherein theat least two coils each are flowed through by a current, wherein thecurrents flowing through the individual coils are out-of-phase and/orhave different current strengths.
 17. Method pursuant to claim 15,wherein the current flowing through the coil arrangement is modified asa function of time.
 18. Method pursuant to claim 15, wherein the coilarrangement is cooled.
 19. Method pursuant to claim 14, wherein theworkpiece is electrically conductive and subjected to current throughflow.
 20. Method pursuant to claim 14, wherein the workpiece is cooled.21. Method pursuant to claim 14, wherein the compressive and/or tractiveforces are applied to the workpiece for the purpose of transportingand/or forming the same.
 22. Device for applying compressive and/ortractive forces on a rod-shaped workpiece comprising electricallyconductive and/or magnetizable material, the device comprises: a coilarrangement that is adapted to be acted upon by current for generating amagnetic field comprising a gradient pointing in the direction of theforce to be applied on the workpiece.
 23. Device pursuant to claim 22,wherein the coil arrangement comprises at least two coils, which can beacted upon by a current that can be adjusted individually for each coilby means of a control unit.
 24. Device pursuant to claim 23, wherein thecoils are arranged around a workpiece path in a concentric manner and inthe axial direction of the rod-shaped workpiece at a distance from eachother, wherein along said path compressive and/or tractive forces aresupposed to be applied on the workpiece.